1. Field of the Invention
The present invention relates to a roll or roll cover for use in a papermaking machine.
2. Description of the Related Art
Wearing, loading and impact resistance are all important properties of rolls or roll covers utilized in the modern papermaking industry. For example, advanced calendering rolls in the modern papermaking industry must be formed such that they are capable of running at higher speeds, higher loads and at higher temperatures and yet have a long life expectancy.
Hard-nip and soft-nip calendering rolls treat paper differently. For example, strength properties and uniformity, especially for newsprint, are better preserved with soft calendering rolls. While soft calendering is currently used on machine-finished coated (MFC) papers, uncoated supercalendered (SC) are supercalendered using harder rolls to obtain the desired finish. Many versions of such cover formulations have been developed individually to optimize the roll's performance for different applications. For example, different types of fillers, reinforcement fibers and chemical resin systems may be utilized.
While adding more filler or reinforcement fibers or using a high glassy transition temperature (Tg) resin system will increase cover hardness and improve abrasion resistance, it typically reduces the cover's impact strength, as well as other crucial nip mechanisms significantly. In contrast, improvement of the impact strength of the cover by use of a low Tg resin system or a decreased quantity of fillers or fibers results in a reduction in the cover's abrasion resistance and a dramatic drop in the temperature at which the cover can effectively operate. A change in the type of fillers or fibers or in the amount of such fillers or fibers used typically results in a high cost in both inventory and manufacturing.
What is needed in the art is a roll or roll cover for a papermaking machine which is formed such that one specific property, such as hardness, is modified while the remaining physical properties beneficial for optimal product performance are maintained.